The present invention relates to silica particles for polishing usefully available in forming a metal wiring layer in a semiconductor integrated circuit for smoothing a surface of a substrate thereof and a polishing agent (or a polishing material) containing the particles for polishing.
Various types of integrated circuits are used in computers and various types of electronic equipments, and a higher degree of integration is required in association with the tendency for higher performances of the circuits.
In the circumstances as described above, multi-layered wiring is used, for instance, in semiconductor integrated circuits to improve the integration degree of semiconductor integrated circuits, and the multi-layered wiring is usually manufactured by forming a thermally oxidized film as a first insulating film on a substrate comprising, for instance, silicon; then forming a first wiring layer comprising, for instance, an aluminum film; coating an inter-layer insulating film comprising, for instance, a silica film or a silicon nitride film by means of such methods as the CVD method or plasma CVD method; forming a silica insulating film for planarizing the inter-layer insulating film by means of the SOG method; coating a second insulating film on the silica insulating film, if required; and finally forming a second wiring layer.
In the wiring comprising an aluminum film is sometimes oxidized with the resistance value increased in spattering for forming the multi-layered wiring, which may in turn causes a conduction fault. Further as the wiring width can not be made smaller, there has been a limit in forming an integrated circuit with a higher integration degree. Further, recently in a long range wiring such as a clock line or a data bus line, the wiring resistance becomes larger in association with increase of the chip size, and an electric signal propagation delay time (RC delay time=resistancexc3x97capacity) disadvantageously increases. To cope with this problem, it is required to provide wiring with a material having a lower resistance value.
It has also been proposed to use Cu in place of Al or aluminum alloy used in the conventional technology for wiring, and for instance, there has been known a method, in which a wiring groove is previously prepared in an insulating film on a substrate and then a Cu wiring is formed by the electrolytic plating method or the CVD method.
In the wiring pattern formation using such material as Cu, machining by the dry etch method can hardly be performed, so that the Damascene process using a chemical and mechanical polishing method (described as CMP method hereinafter), and in this case, a wiring groove is previously formed in an insulating film on a substrate, and then a copper wire is buried in the wiring groove by means of the electrolytic plating method or the CVD method with an upper edge face polished by the CMP method for planarizing it to form the wiring. For instance, an inter-wiring layer film (an insulating film) is formed on a surface such as a silicon wafer with a groove pattern for metal wiring formed thereon, and further a barrier metal layer comprising, for instance, TaN is formed by the spattering method or the like, if necessary, and finally a copper wire for the metal wiring is provided by the CVD method or other appropriate method. When the barrier metal layer comprising such material as TaN is provided, such troubles as lowering of the insulating capability of the inter-layer insulating film caused by dispersion of or corrosion by copper or other impurities can be prevented, and further adhesiveness between the interlayer insulating film and copper can be enhanced.
Then the unnecessary copper metal film and barrier metal film (which may sometimes be called as a sacrifice layer) formed outside the groove are polished by the CMP method, and at the same time the upper surface of the substrate is planarized as much as possible to leave a metal film in the groove, and thus the copper wiring and circuit pattern being formed.
In the CMP method, generally a polishing pad is placed on a round platen having a rotating mechanism, a work to be polished is rotated in the state where a polishing material is being dripped from a position above a center of the polishing pad, the work is pressed and contacted to the polishing pad, and the copper and barrier metal layers on the common plane are polished away.
As irregularities due to a groove pattern for wiring formed on the under insulating film is present on a surface of the work to be polished, the surface is required to be polished down to the common plane by removing mainly the convex sections for obtaining a planarized surface.
The polishing material used in the CMP method generally comprises spherical particles for polishing comprising oxides of metals such as silica and alumina and having the average particle diameter of about 200 nm; an oxidizing agent for raising the rate of polishing the metals used for wiring and circuit patterns, and an additive such as an organic acid; and a solvent such as deionized water.
In the conventional technology of polishing with silica or alumina, there is the disadvantage that scratches such as flaws or stripes still remain, or are newly generated after the polishing process.
Japanese Patent Laid-Open Publication No. HEI 9-324174 discloses the composite particles comprising organic materials and inorganic materials usefully available for suppressing generation of scratches, and the composite particles contain an organic polymer skeletal structure and a polysiloxane skeletal structure containing in the molecular structure an organic silicon directly and chemically bonding to at least one carbon atom in the organic polymer skeletal structure, and a content of SiO2 constituting the polysiloxane skeletal structure is 25 weight % and more.
Hardness of the composite particles comprising organic and inorganic materials described above varies according to a content of SiO2 constituting the polysiloxane skeletal structure, and in a case where a content of organic polymer is large and a content of SiO2 is small, scratches are generated little, but the required polishing rate is low. On the contrary, in a case where a content of organic polymer is small and a content of SiO2 is large, the polishing rate is high, but starches will easily be generated. Even if the SiO2 content is made large within the range where scratches are not generated, the sufficient polishing rate can not be achieved, which is a bottleneck in this technology.
It is an object of the present invention to provide particles for polishing capable of suppressing generation of the so-called scratches and also polishing and planarizing a surface of a substrate at a sufficient polishing rate and also to provide a polishing agent or a polishing material containing the particles for polishing.
The silica particles for polishing according to the present invention are characterized in that the average particle diameter is in the range from 5 to 300 nm and the carbon content is in the range from 0.5 to 5 weight %.
The silica particles for polishing should preferably have the 10%-compressive elasticity modulus in the range from 500 to 3000 kgf/mm2. The Na content of silica particles for polishing should preferably be less than 100 ppm as converted to Na.
A polishing agent or a polishing material according the present invention contains the silica particles for polishing.
[Particle for polishing]
The average particle diameter of the silica particles for polishing according to the present invention is preferably in the range from 5 to 300 nm, and more specifically in the range from 10 to 200 nm, although it depends on such factors as required polishing rate, and polishing precision. When the average particle diameter is less than 5 nm, stability of the dispersion liquid of silica particles is apt to become unstable, and the particle size is too small to realize the sufficient polishing rate. When the particle size is more than 300 nm, scratches will remain and the desired smoothness may not be achieved, although it depends on types of substrates and insulating films.
A content of carbon in the silica particles for polishing should preferably be in the range from 0.5 to 5 weight %, and more specifically in the range from 0.7 to 4 weight %. When the carbon content is less than 0.5 weight %, for instance, residual alkoxy group is not present, siloxane bonding proceeds, the particles are hard (with the high elasticity modulus), and therefore scratches remain or are generated anew even though the polishing rate is high, so that smoothness of the polished surface is insufficient. On the other hand, when the carbon content is over 5 weight %, a quantity of residual alkoxy group increases, so that the particles become relatively soft (with the low elasticity modulus) and a sufficient polishing rate can not be achieved.
The 10%-compressive elasticity modulus of the silica particles for polishing should preferably be in the range from 500 to 3000 kgf/mm2, and more preferably in the range from 600 to 2000 kgf/mm2. When the 10%-compressive elasticity modulus is less than 500 kgf/mm2, the particles are relatively soft, so that a sufficient polishing rate can not be achieved. When the 10%-compressive elasticity modulus is over 3000 kgf/mm2, the particles are too hard, and scratches remain or are generated anew after polishing and smoothness of the polished surface is insufficient even though the polishing rate is high.
The method of assessing the 10%-compressive elasticity modulus employed in the present invention is as described below. The 10%-compressive elasticity modulus is obtained with a micro compression tester (manufactured by Shimazu Seisakusho K. K.: MCTM-200) as a tester and with one particle having the particle diameter of D as a sample by applying a load at a prespecified loading rate, deforming the particles until the compression displacement reaches 10% of the particle diameter, measuring the load and the compression displacement (mm) at the 10% displacement, and substituting the particle diameter, and the measured compression load and compression displacement into the following equation:
K=(3/{square root over ( )}2)xc3x97Fxc3x97Sxe2x88x923/2xc3x97Dxe2x88x921/2 
wherein K indicates the 10%-compressive elasticity modulus (kgf/mm2), F indicates a compression load (kgf), S indicates a compression displacement (mm), and D indicates a particle diameter (mm).
The particle diameter of silica particles for polishing allowable in the present invention is small, namely in the range from 5 to 300 nm, so that the particle diameter can hardly be measured with the tester, and even if the measurement is possible, the precision may be insufficient. Therefore, in the examples described below, the samples are prepared in the same manner as that employed for manufacturing the silica particles for polishing except the point that particles with particularly large diameter are used as the samples. Specifically 10 pieces of particles having the particle diameter in the range from 2 to 3 xcexcm dried for 24 hours under 105xc2x0 C. were selected, and an average value measured thereof was used as the 10%-compressive elasticity modulus for the silica particles for polishing.
Na content in the silica particles for polishing as converted to Na in SiO2 should be less than 100 ppm, preferably less than 50 ppm, and more preferably less than 20 ppm. When the Na content is over 100 ppm, Na remains on the substrate polished with the silica particles, and the Na may cause insulation fault or short circuitry in a circuit formed on the semiconductor substrate, and in that case the dielectric constant of a film provided for insulation (insulating film) drops while impedance in the metal wiring increases, which may in turn cause such troubles as a response delay or increase in power consumption. Further sometimes Na ions may move (disperse), which may cause the troubles as described above when the substrate is used for a long time.
[Preparation of silica particles for polishing]
There are no specific restrictions over the method of manufacturing the silica particles for polishing according to the present invention on the condition that particles with the carbon content as described above and preferably with a prespecified 10%-compressive elasticity modulus are obtained. Especially the method disclosed by the present applicant in Japanese Patent Laid-Open Publication No. HEI 11-61043 can advantageously be used for this purpose, and in this method, monodispersed silica particles with the average particle diameter in the range from 5 to 300 nm are obtained during the process for obtaining short fibrous silica.
The method of manufacturing polyorganosiloxane disclosed in Japanese Patent Laid-Open Publication No. HEI 9-59384 can advantageously be used, and in this method particles with the average particle diameter in the range from 5 to 300 nm can be obtained.
A specific method of manufacturing silica particles for polishing is described below.
The silica particles for polishing are obtained by hydrolyzing one or more alkoxysilanes generally expressed by the following formula [1] and then subjecting the particles to hydrothermal processing under a temperature of 150xc2x0 C. or less according to the necessary:
XnSi(OR)4xe2x88x92nxe2x80x83xe2x80x83(1)
wherein X indicates a hydrogen atom, a fluorine atom, an alkyl group having 1 to 8 carbon atoms, an aryl group, or a vinyl group; R indicates a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, an aryl group, or a vinyl group; and n is an integral number from 0 to 3.
The alkoxysilanes expressed by the formula [1] include tetramethoxysilane, tetraethoxysilane, tetraisopropoxysilane, tetrabutoxysilane, tetoraoctylsilane, methyltrimethoxysilane, methytriethoxysilane, methyltriisopropoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, ethyltriisopropoxysilane, octyltrimethoxysilane, octyltriethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, trimethoxysilane, triethoxysilane, triisopropoxysilane, fluorotrimethoxysilane, fluorotriethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, diethyidimethoxysilane, diethyidiethoxysilane, dimethoxysilane, diethoxysilane, difluorodimethoxysilane, difluorodiethoxysilane, trifluoromethyltrimethoxysilane, and trifluoromethyltriethoxysilane.
Hydrolysis of the alkoxysilanes as described above is performed under the existence of water, an organic solvent, or a catalyst.
The organic solvents available for this purpose include, but not limited to, alcohols, ketones, ethers, and esters, and more specifically the organic solvents include, for instance, alcohols such as methanol, ethanol, propanol, and butanol; ketones such as methylethyl ketone, and methylisobutyl ketone; glycol ethers such as methyl cellosolve and ethyl cellosolve, and propylene glycol monopropyl ether; glycols such as ethylene glycol, propylene glycol, and hexylene glycol; and esters such as methyl acetate, ethyl acetate, methyl lactate, and ethyl lactate.
The catalyst includes basic compounds such as ammonia, amine, alkali metal hydrides, quarternary ammonium compounds, and amine-based coupling agents. The alkali metal hydrides may be used as a catalyst, but in that case, hydrolysis of an alkoxy group in the alkoxysilane is promoted, so that a quantity of residual alkoxy groups (carbon) in the obtained particles decreases and the 10%-compressive elasticity modulus becomes higher than 5000 kgf/mm2, and therefore the polishing rate is high, but scratches may be generated anew, and further Na content becomes disadvantageously high.
A quantity of water required for hydrolysis of the alkoxysilane is in the range from 0.5 to 50 moles per mole of Sixe2x80x94OR group constituting alkoxysilane, and preferably in the range from 1 to 25 moles. Further the catalyst should preferably be added at a rate of 0.005 to 1 mole per mole of alkoxysilane, and more preferably at a rate of 0.01 to 0.8 mole.
Hydrolysis of alkoxysilane is performed under the atmospheric pressure at a temperature lower than a boiling point of the used solvent, and more preferably at a temperature 5 to 10xc2x0 C. lower than the boiling point. When a heat-resistant and such pressure-resisting vessel as autoclave is used, the reaction can be performed at a temperature higher than the values above.
When hydrolysis is performed under the conditions as described above, polycondensation of alkoxysilane proceeds three-dimensionally, and silica particles for polishing with the particle diameter in the range from 5 to 300 nm can be obtained. Next, when alkoxysilane is hydrolyzed again together with the obtained particles, larger silica particles for polishing with the particle diameter in narrow range can be obtained.
Further the obtained silica particles may be subjected to the hydrothermal processing under the temperature of 150xc2x0 C. or less, if necessary. By performing this hydrothermal processing, it is possible to reduce the carbon content to a required level or to improve the 10%-compressive elasticity modulus to a required value.
When the temperature under which the hydrothermal processing is performed exceeds 150xc2x0 C. and especially exceeds 250xc2x0 C., although it depends on the concentration of ammonia etc. coexisted, sometimes not monodispersed particles, but short fibrous silica particles each comprising several pieces of particles bonding to each other two-dimensionally may be obtained. When the short fibrous silica particles are used as polishing material, sometimes scratches may be generated, but dishing (excessive polishing) can be suppressed.
[Polishing agent (or polishing material)]
The polishing material according to the present invention is prepared by dispersing the silica particles for polishing described above in a dispersion medium. Although water is used as the dispersion medium, also such alcohols as methyl alcohol, ethyl alcohol, and isopropyl alcohol may be used according to the necessity, and in addition such water-soluble organic solvents as ethers, esters, and ketones may be used.
A concentration of silica particles for polishing in the polishing material should preferably be in the range from 2 to 50 weight %, and more preferably in the range from 5 to 30 weight %. When the concentration is less than 2 weight %, the concentration is too low for some types of substrates and insulating films, and in that case the polishing rate is too low to provide high productivity. When the concentration of silica particles is over 50 weight %, stability of the polishing material is insufficient, so that the polishing rate or the polishing efficiency can not further be improved, and sometimes dried materials may be generated and deposited on the substrate during the process of feeding a dispersion liquid for the polishing process, which may in turn generate scratches.
Any of such known additives as hydrogen peroxide, peracetic acid, urea peroxide, and a mixture thereof may be added to the polishing material according to the present invention, although the appropriate additive varies according to a type of a work to be polished. When such additive as hydrogen peroxide is used, the polishing rate can effectively be improved in the case of metallic work to be polished.
Further, such acids as sulfuric acid, nitric acid, phosphoric acid, and fluoric acid; sodium salts, potassium salts, and ammonium salts of these acids; and a mixture thereof may be added to the polishing material according to the present invention. When a plural types of works are polished with these additives, by making higher or lower the polishing rate for a particular work comprising specific components, finally a planarized surface can be obtained by polishing.
As other additives, imidazole, benzotriazole, benzotiazole, or the like may be used to prevent corrosion of a substrate by forming an immobilized layer or a dissolution suppressing layer on a surface of the metallic work to be polished.
Further such organic acids as citric acid, lactic acid, acetic acid, oxalic acid, and phtalic acid, or a complex forming agent for these organic acids may be added to the polishing material to disturb the immobilized layer.
Cationic, anionic, nonionic, or amphoteric surfactant may be added to the polishing material for improving dispersibility or stability of a slurry of the polishing material.
Further, pH of the slurry of polishing material may be adjusted by adding an acid or a base according to the necessity to improve the effect of adding each of the additives as described above.
With the present invention, since the silica particles for polishing contain a prespecified content of carbon and also have elasticity, the polishing rate with the polishing material comprising the particles for polishing can easily be controlled without any scratch generated, and a surface of a substrate can be polished into the extremely planarized and smooth state. Further the silica particles substantially contain no Na content, so that Na is not deposited on a surface of a semiconductor substrate or an oxidized film, and therefore the silica particles for polishing according to the present invention are extremely useful in planarizing a substrate, especially in forming a metal wiring layer in a semiconductor integrated circuit.